Re: anyone know where I can find a service manual for Disk II

[Silicon Sam <SiliconSam@gmail.com>]

On Apr 10, 5:22 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
>
> >   Not sure, but since the sine wave was a slow one, I would say it
> > only had to wobble once per revolution.  The object was to write a
> > signal from 1 track to the other, and measure the track in between.
> > Obviously the disk can sit still and the head move back and forth
> > between tracks while writing.  But it would have to be a mechanism far
> > more precise than the cam that Shugart and Alps used.
>
> >   Yes, there are several signals on the disk, this is just how they
> > made the cats eye recording.
>
> I'm having a hard time seeing how a wobbled recording makes a
> cat's eye diagram.
>
> It seems like the display would be amplitude modulated at the wobble
> frequency when off-center in either direction and amplitude modulated
> at twice the wobble frequency when on-center, assuming that the
> amplitude of the wobble was a bit more than a track.
>
> And I agree that this would require a special drive to record--
> either one with a voicecoil actuator or (kind of fun) one with
> an eccentric spindle.  ;-)
>
> The dual-frequency recording I described could actually be made
> in a non-phase-coherent way, with a single headed drive.  One
> frequency would be recorded with the track positioned +0.75
> track, and the other at -0.75 track.  The only problem would
> be ensuring that the edge of the erase head on the second track
> written didn't put the "equal amplitude" point off the center
> of the nominal track.
>
> -michael
>
> NadaPong: Network game demo for Apple II computers!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."

  A cats eye is a signal that is very strong, then drops off to
nothing then back strong again.  Like a sine wave on AC voltage.  What
you see when you look at track 16 is a strong amplitude signal when
the signal written is spot on track 16, and it drops off the as the
signal get weak as it moves over to track 15 or towards track 17.  It
returns again as the disk spins and the amplitude of the signal gets
stronger, then weaker, then non-existent when it is spot on track 15
or 17.  Repeat as long as the disk spins.  Adjust the head until the
highest peak of the signal is the strongest.  Page 3.16 of the disk2-
tech manual mentioned above.

  About the best way I can describe it, but I can try again...

Raymond